Properties of Neurons Ch 2 & 3

What are the 2 parts of the Nervous System?

The Central Nervous System and Peripheral Nervous System (CNS & PNS)

What do the CNS and PNS consist of?

Brain and Spinal Cord (CNS)

Nerves that send signals to the rest of the body (PNS)

What are the 2 types of cells in the Nervous System?

Neurons and Glia

What are some facts about neurons?

They are excitable and can communicate chemically or electrically

What are some facts about glia?

They are not excitable. Their role is to maintain homeostasis, support neurons, and form myelin.

What are the two types of stains we have studied?

The Nissl and Golgi stains?

What does the Nissl stain do?

Labels rough ER, the cell body, nucleolus, and glia

What are some pros of the Nissl stain?

It can visualize all neurons, some glia; you can see the cytoarchitecture

What are some cons of the Nissl stain?

You can only see the cell body, not the axons or dendrites. This means you can only see the number of neurons and the density of their packing.

What does the Golgi stain do?

They label axons and dendrites (dendrites branching). This is a silver solution.

What are some pros for the Golgi stain?

You can see the entire neuron and some glia

What are some cons of the Golgi stain?

Only about 10% of cells get labeled (not good for talking about density and packing).

What are the two names in neuroscience history we have looked at?

C. Golgi and Santiago Ramón y Cajal.

What did Golgi believe in?

He believed the brain and spinal cord were interconnected by a single cytoplasm.

Who debunked Golgi’s belief?

S. Ramón y Cajal did. He created the neuron doctrine, showing close but small gaps, proving there are a lot of them all working together.

What are the 4 types of Glia we have covered?

Astrocytes, oligodendrocytes, Schwann cells, and microglia.

What are some facts about Astrocytes?

They are the most abundant form of glia, and they regulate extracellular space.

In what ways do Glia regulate extracellular space?

Removing and recycling neurotransmitters, scavenging excess ions, maintaining pH, and regulating movement between blood and extracellular fluid.

What are some facts about Oligodendrocytes and Schwann cells?

They wrap around axons to form Myelin. Oligodendrocytes in the CNS and Schwann cells in the PNS.

What are some facts about Microglia?

They have many important functions, including specialized macrophages. They are the immune system of the NS. They are very important for development and disease states (Dr. Monique Mendes)

What are the 4 parts of neuron anatomy?

Dendrites, Cell body, Axons, and axon terminals

What is the role of the dendrites?

They are the site of receptors. Receive input via receptors and have dendritic spines to increase their surface area.

What is the role of the cell body (soma)?

Organelles and integration

What is the role of axons (myelin coverage)?

They conduct action potentials.

What is the role of axon terminals?

Release output via neurotransmitter release (they innervate other cells).

How are neurons compared in regard to other cell types?

They are similar to other cell types.

In what ways are neurons similar to other cell types

Most organelles are the same (Cell body), the axon and dendrites contain few organelles, the axon terminal contains lots of mitochondria and vesicles, and the basic cellular processes are the same.

What are 4 ways that neurons are unique?

1) Action potentials (excitable)

2) Form synapses with other neurons (join/conjoin)

3) There are specialized membrane proteins in each part of the neuron

4) Have an extensive/organized microtubule system (parallel/train tracks)

What type of transport relies on this extensive/organized microtubule system?

Axoplasmic Transport

What molecule does Anterograde transport use?

Kinesin

What molecules does retrograde transport use?

Dynein

Describe the process of transporting molecules on this microtubule system?

Kinesin or dynein latches onto the microtubule like a train car. Kinesin or dynein holds a vesicle (cargo) and goes down the microtubule to transport it.

What is a neurite?

It is the axon + the dendrites extending from the cell body

What are the three ways of classifying a neuron from it’s neurites?

Multipolar, bipolar, and unipolar

What is a multipolar neuron?

Most neurons are multipolar (2+), lots of input on these.

What is a bipolar neuron?

It is a neuron with 2 neurites. Bipolar neurons exist in some sensory pathways, such as the retina, taste, and the ears.

What is a unipolar neuron?

Unipolar cells exist in peripheral sensory nerves, including touch, pain, and temperature.

What are some other classifications of neurons?

Function (motor, sensory, interneuron), shape, presence of dendritic spines, axon length, and neurotransmitter-related gene expression

Can ions readily cross the hydrophobic phospholipid bilayer?

No, they cannot.

How are ion’s in neurons distrubted?

Ions are unevenly distributed, with a negative resting membrane potential of -65 mV, comparing the inside vs. the outside.

How do the charges not intermingle?

The plasma membrane separates the charges so they don’t intermingle.

What sets up/maintains the distribution of ions?

Pump channels do.

What is a common pump that is always talked about?

Sodium - Potassium Pumps

What is the distribution of ions in a sodium - potassium pump?

2 K+ goes inside the cell (higher K+ inside), 3 Na+ goes outside the cell (higher Na+ outside)

What happens to the cell in a sodium - potassium pump?

The cell gets a little more negative.

What allows for diffusion?

Ion channels allow for diffusion

What type of channels exist in neurons?

Na+, K+, Ca2+, and Cl- channels. Some are gated, and others are always open (leak channels).

Are ion channels selective?

Yes, ion channels are selective

In what ways are ion channels selective?

Some are selective for ions of a certain charge (charge channels). Many are selective for one particular ion (ion-coded).

What’s an example of an ion-selective channel?

All ions have water attached; channels have carbonyl oxygens that pop off the water and allow that specific ion in. Depending on the ion, it may or may not reach the carbonyl oxygens to be allowed through.

What type of forces act on ions?

Concentration gradients and electrical gradients

What way does concentration gradient flow?

High to low concentration

How does an electrical gradient work?

Depending on the charge of the ion, it will always move toward the resting membrane potential (in the middle).

What is the charge of the extracellular fluid (outside)?

Positive charge.

What is the charge of the cytosol (inside)?

Negative charge.

For direction dictated by electrical gradient (at -65 mV), what way do the following ions flow: K+, Na+, Ca2+, Cl-?

K+: Out to in

Na+: Out to in

Ca2+: Out to in

Cl-: In to out

What do we use to confirm direction if concentration and electrical gradient are opposing (electrochemical gradient)?

The Nernst equation!

What is the Nernst equation measuring?

Allows you to calculate the equilibrium potential of the ion, the charge of the cell at which the direction of ion movement switches (when electrical and chemical gradients become equal).

In the Nernst equation, how many ion channels are open?

One channel is open.

When ion channels for a specific ion open and stay open, what happens to the charge?

The ion will drive the charge of the cell to its equilibrium potential.

What are the four ions’ rough equilibrium potentials at normal temperature?

K+ = -80 mV

Cl- = -65 mV

Ca2+ = 123 mv

Na+ = 62 mV

What happens when ion channels open at the resting membrane potential (-65 mV)?

K+ (-80 mV): In to out

Na+ (62 mV): Out to in

Ca2+ (123 mV): Out to in

Cl- (-65 mV): Equilibrium, no net movement

What are some things to remember about the Nernst equation?

Most ion channels are usually closed; sometimes multiple types of ion channels are open. The speed of ion movement is proportional to the difference between the resting membrane potential and the equilibrium potential.

What’s a good comparison when talking about speed of ions?

Ca2+ vs Na+: (Calcium rushes in, Sodium slowly goes in) (123 mV vs. 62 mV)

So what is the deal when there are multiple ion channels open?

We use the Goldman equation!

What does the Goldman equation do?

Calculates membrane potential and accounts for permeability of multiple ions across the membrane.

What is permeability?

Permeability refers to how many ion channels are open for that ion at that specific time. There are no units, going to be a ratio.

In the Goldman equation, what’s one thing to keep in mind?

For a negative charge like chlorine, you must flip the outside and inside concentrations to account for the negative charge.

What are some facts regarding resting potential?

Em is close to EK+, Em is very close to ECl-, so very little net Cl- movement, different types of neurons have different resting membrane potentials (-65 to -80 mV).

What are the 2 terms regarding membrane potential changes?

Depolarization and Hyperpolarization

What is depolarization?

The cell is becoming less negative relative to its resting membrane potential (-65 to -40 mV).

What is hyperpolarization?

The cell becomes more negative relative to its resting membrane potential (-65 to -80 mV).

What ion has the largest influence on resting membrane potential?

Potassium (K+) does.

What buffers extracellular K+

Astrocytes

How do astrocytes buffer extracellular K+

They can take up excess K+ when levels are high and can release K+ when levels are low.

What limits potassium flow into the extracellular fluid?

The blood-brain barrier.